The present invention concerns hydrocarbon soluble thio-bis-(alkyl lactone acid esters) and thio-bis-(hydrocarbyl diacid esters), their method of preparation and their utility, preferably, in hydrocarbon fuel and lubricating systems, as stable sludge dispersants, varnish inhibitors, antioxidants, antiwear agents and lubricity additives.
During the past decade, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants and gasoline, in keeping the engine clean of deposits, and permitting extended crankcase oil drain periods. One category of ashless dispersants involves esters of alkenyl substituted acids, e.g. polyisobutenyl succinic acids, with polyols e.g., pentaerythritol, as taught in U.S. Pat. No. 3,381,022; however, such dispersants oftentimes contain olefinic unsaturation making them susceptible to oxidative degradation especially under high severity conditions such as elevated oil temperatures and extended drain intervals.
A second category involves chloro lactone ester dispersants prepared via the esterification of alkenyl chloro lactone acids with pentaerythritol as taught in U.S. Pat. No. 3,755,173; however, the inherent propensity of such dispersants, or antirust compounds as taught in U.S. Pat. No. 2,279,688 towards elimination of corrosive HCl to give unsaturated products, can promote decomposition of the hydrocarbon lubricant, corrode metal engine parts, and promote varnish deposition on the internal surfaces of the engine.
Thus, the effectiveness of dispersants of either category, particularly at higher temperatures, can be markedly impaired by oxidative degradation. Besides, not only do such systems suffer from instability problems, but the potency of such dispersants oftentimes, owing to inherent limitations in their sludge binding capacity, diminishes with increasing severity of operating conditions. The present invention overcomes the shortcomings of the prior art by designing novel thio-bis-(polyalkyl lactone acid esters) and thio-bis-(hydrocarbyl diacid esters) with enhanced stability and potency. The stabilization of these novel dispersant systems may be ascribable to the lack of unsaturation and/or the presence of sulfide functionality which endow these systems with enhanced stability and antioxidant properties. The enhanced potency may be related, in part, to the macrocyclic and/or macrocyclic-like configuration assumed by the polar sulfur and oxygen (heteroatom) functionality in some of the dispersant molecules. Such circular-like arrangements of ligands endow these novel systems with remarkable binding and/or chelation properties and in some instances, inclusion properties, making these dispersant systems uniquely effective even under high severity conditions.
We propose herein, novel and improved dispersant systems based on host-guest chemistry wherein the polar head of the host molecule (dispersant) assumes or is capable of assuming a macrocyclic-like configuration so that the resulting circular-like array of heteroatoms (e.g. sulfur, oxygen and nitrogen), on the polar head effectively binds guest ions and molecules, including metals and sludge components, within the cyclic-like structure, or between host molecules to form a sandwich-like structure with guest molecules in the middle.